Microfluidic devices require a source of liquid reagents to operate. Typically for emulsion-based systems, these reagents are stored in bottles or tubes which are then connected to the device by the user, with tubing and connectors. This requires complex manipulation of tubing and connectors, creating the potential for waste, due to leaks or operator errors. Reagent leaks and handling contamination are a considerable source of variability in system operation.
By their very nature, microfluidic devices deal in the behavior, precise control, and manipulation of fluids that are geometrically constrained to small scales. To drive fluids across micro-scale features within devices, power must be supplied to move the working fluid(s). Devices can feature micropumps or small-scale external pressure sources, some even harness capillary forces or electrokinetic mechanisms. One approach to generating fluidic motion is the use of servo-driven syringe pumps. These pumps have high fluidic capacitances and often require cumbersome fluidic pre-preparation. The process can result in long settling times and unsteady fluidic transients.
Where using channels of micron scale, there is the ability to manufacture devices that have excellent control over the production, handling, manipulation, merging, and detection of droplets with volumes on the order of picoliters at rates exceeding 100,000 times per second. The source of fluid to be used in a microfluidic device is typically located separately from the device, such as in a syringe, where the fluid is subsequently introduced into the microfluidic device via tubing or another via another source. When a microfluidic device has many fluid inputs and outputs connecting to any syringes with many ports for tubing, the complexity of the device increases along with the cost of fabrication, assembly and operation.